It is known to improve the flameproof character of polycarbonates by adding alkali metal salts. (See, for example, U.S. Pat. Nos. 3,775,367 (Le A 12 278+Le A 14 723) and 3,836,490 (Le A 13263+Le A 13619) and British Pat. No. 1370744 (Le A 13 999) incorporated herein by reference.)
It is also known to improve the flameproof character of polycarbonates by adding organic chlorine compounds (see, for example, U.S. Pat. No. 3,357,942, DT-OS (German Published Specification) 2,122,300, French Patent Specification No. 1,439,030 and DT-OS (German Published Specification) No. 2,153,101 and DT-OS (German Published Specification) No. 2,243,226).
It is also known to improve the flameproof character of polycarbonates by adding organic bromine compounds.
It is also known to improve the flameproof character of polycarbonates by means of mixtures of organic chlorine compounds and certain inorganic salts (see, for example, DT-OS (German Published Specification) No. 2,013,496; suitable organic chlorine compounds which are mentioned are, inter alia, tetrachlorophthalic anhydride).
The synergistic effect of fluorinated polyolefins in flame-repellent polycarbonate molding compositions is also known (see, for example, DT-OS (German Published Specification) No. 2,535,262 and U.S. Pat. No. 3,651,174).
However, the polycarbonate molding compositions of low flammability, according to the instant invention, were not obvious since no additive combinations have been known hitherto which, after admixing such small amounts by weight as are necessary for the additive combinations according to the invention, already give polycarbonate molding compositions of the burning class V-O according to UL 94 at wall thicknesses of 1/8" and 1/16". The admixing, claimed according to the invention of tetrahalogenophthalimides of the general formula (I) or (II) is thus particularly advantageous because compounds of this class of substances are very stable to heat, of low volatility, and resistant to saponification and can be readily mixed into the polycarbonate.